According to the influential Model Penal Code (MPC), a person’s mental state (known as mens rea, from the Latin) when he or she commits a crime determines that person’s culpability. For example, it’s worse to commit an act knowingly (with practical certainty about some legally relevant circumstance) than recklessly (with conscious awareness of a substantial risk that the circumstance exists or will occur).

Recent scholarship, however, has shown that people have difficulty distinguishing between the legally defined knowing and reckless states. This has serious implications because the differences in punishment depending on the defendant’s mental state can be substantial. And it has led some to question whether there is a genuine difference between these two mental states as the MPC defines them. Most criminal law theorists believe there is a difference, but the recent scholarship called this distinction into question.

Could neuroscientific technology help determine if knowledge and recklessness are discrete mental states? A new study co-authored by Penn Law professor Stephen J. Morse and a number of other researchers from neuroscience, law, and philosophy, led by neuroscientist Read Montague and law professor Gideon Yaffe, shows that brain imaging data can be used, with high accuracy, to predict a participant’s mental state.

“Scientific evidence for (or against) biologically based and brain-based distinctions of knowing and reckless mental states, and the boundary that may separate them,” the authors of the study write, “could help us either to refine or to reform the ways criminal responsibility is assessed.”

In their study, the authors used functional magnetic resonance imaging (fMRI) to determine how the MPC’s “culpable mental states” of knowledge and recklessness are associated with different brain states and, if so, which specific brain regions are involved.

For the experiment, 40 participants were asked to undergo fMRI while they decided whether or not to carry a hypothetical suitcase, which could have contraband in it, through a checkpoint. By varying the probably that the suitcase contained contraband, the researchers were able to put participants into either a knowing mental state (since they knew the suitcase had contraband) or a reckless one (since they did not know if the suitcase had contraband in it, but were aware that there was a high risk of that being true).

The researchers found that they were able to predict with a high degree of accuracy whether a person was in a knowing or reckless state, and were also able to associate those mental states with unique functional brain patterns.

“This study is a first step in understanding how the legally defined concepts of “knowledge” and “recklessness” map onto different brain states and shows, as proof of principle, that it is possible to predict which legally defined mental state a person is in,” the authors write.

The researchers also see this work contributing to how certain recognized mental disorders, such as a schizoaffective disorder, might impact a person’s mental state.

“Understanding more about the way our brains distinguish between legally relevant circumstances in the world has the potential to improve what, up until now,” the authors write, “has been the law’s guesswork about the ways in which certain mental conditions might impact criminal responsibility.”

They caution, however, that the imaging in the experiment was conducted at the moment of decision making by the participant — criminal defendants will not be in an fMRI scanner at the moment they commit a crime. The researchers do not currently know if it is possible to classify someone’s brain state months, or even years, after the act.

Although the study is only a first attempt to do this kind of work and the sample is relatively small, it does suggest that the MPC’s distinction between knowledge and recklessness may be valid.

Nonetheless, “Even if several future studies confirm what we have observed here, that knowledge and recklessness are associated with different brain states, if human jurors cannot distinguish them behaviorally, then one may still ask whether they should be considered relevant to assessments of criminal liability,” the authors write. “Our results here do not settle this question.”

Professor Stephen J. Morse's research examines the intersections of law and neuroscience.